In radio frequency transmission systems, signals that are transmitted between a transmitter and a receiver can deteriorate or be lost due to multi-path fading or shadowing. In these cases, diversity receivers may provide an improvement. Diversity receivers comprise two or more separate receiver circuits, each with its own antenna, and a combiner that combines the signals received by the individual antennas. Since the signals propagate from the transmitter to the individual antennas via different transmission channels and since each of the transmission channels experiences different multi-path fading and shadowing, a more accurate signal can be produced when combining the signals received by the individual antennas.
In one of many ways, diversity receivers receive signals which are so-called multi-carrier signals. Multi-carrier signals are produced by splitting a signal to be transmitted into a plurality of sub-signals, each of which is transmitted separately on an individual frequency carrier. A receiver receives the sub-signals from each of the carriers and recombines them to reproduce the original signal. In multi-carrier transmission systems, diversity receivers take advantage of the fact that the multi-path fading and shadowing on the different antennas is not the same so that, when one antenna receives a multi-carrier signal that comprises faded sub-signals, chances are that another antenna receives these sub-signals without fading. Combining the multi-carrier signals received by the individual antennas can thus mitigate fading.